REMEDIATION METHODS AGAINST LIQUEFACTION WHICH CAN BE APPLIED TO EXISTING STRUCTURES - Earthquake Geotechnical Engineering - page 376

CHAPTER 16
REMEDIATION METHODS AGAINST LIQUEFACTION WHICH CAN BE
APPLIED TO EXISTING STRUCTURES

Susumu Yasuda
Department of Civil and Environmental Engineering, Tokyo Denki University, Japan
[e-mail]

Abstract. Many kinds of remediation methods against liquefaction have been developed and
appliedtostructuressincethe1964Niigataearthquake.However,onlyafewremediationmethods
which can be applied to existing structures have been developed. A huge number of old structures
in the world have not been treated to resist liquefaction. Recently, several new techniques to treat
existing structures have been developed. In this paper, restrictions to be considered in remediation
techniques for existing structures are discussed first.Then recent remediation methods for existing
raft foundations, pile foundations, embankments, sea walls, and buried structures are introduced
together withtheprinciple ofremediation. Remediation methodsforliquefaction-induced floware
also introduced.

1. Introduction

During the 1964 Niigata earthquake, many oil tanks settled due to liquefaction in Japan.
However, some tanks had no damage because their foundation ground had been com-
pactedbyvibro-floatation(Watanabe,1966).Thiswasthefirsttimethattheeffectiveness
of compaction of the ground against liquefaction was recognized. Based on this experi-
ence, the ground under several new tanks was improved at a factory in Hachinohe City.
Shortly after the improvement work, the 1968 Tokachi-oki earthquake hit the site and
demonstrated the effectiveness of the compaction method again (Ohsaki, 1970). After
these events, many kinds of remediation methods were developed. However, almost all
the methods developed applied to new structures. The Japanese Geotechnical Society
published a topic on remediation measures against liquefaction in 1993 in Japanese, and
translated it into English in 1998 (JGS, 1998). Almost all the methods introduced in the
bookwereremediationmethodsfornewstructures.Themainprinciplewassoilimprove-
ment to prevent liquefaction by densification methods, such as the sand compaction pile
method,thevibro-floatationmethod,etc.Thesoilimprovementtechniqueswerenoteasy
to apply toexistingstructures.

Though many kinds of remediation methods against liquefaction were developed and
applied to new structures, a huge number of old structures have not been treated to
resist liquefaction. Remediation of the old structures is quite important. For example,
many oil storage tanks, river dikes, and timber houses which are not treated exist in
large cities. Liquefaction-induced damage to the not-treated structures is a serious con-
cern. Recently, several unique soil improvement techniques which can be applied to the
ground under existing structures have been developed. Moreover, several techniques to
strengthenstructurestopreventtheircollapseifthegroundshouldbeliquefiedhavebeen